Means eor neutralizing eoreign inter-eerence



April 21, 1925. 1,534,013-

H. NYQUIST MEANS FOR NEUTRALIZING FOREIGN INTERFERENCE Filed May 19, 1922 U o INVENTOR. J1,-

7 /w TORNEY Patented Apr. 21, 1925.

UNITED STATES PATENT OFFICE.

HARRY NYQUIST, OF ELMHURST, NEW YORK, AS'SIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MEANS FOR NEUTRALIZING FOREIGN INTERFERENCE.

Application filed May 19, 1922.

To all whom it may concern.-

Be it known that I, HARRY NYQUIs'r, residing at Elmhurst, in the county of Queens and State of New York, have invented certain Improvements in Means for Neutralizing Foreign Interference, of which the following is a specification.

This invent-ion relates broadly to the method of and means for neutralizing the effects of foreign interference in grounded telegraph circuits, particularly that form of interference effect which arises from a difference of ground potential between the terminals of a circuit.

In the operation of grounded telegraph circuits, trouble arises from a difference of ground potential between the ground con nections at the terminals of such circuits. which manifests itself in adistortion of the signals being transmitted'over the line circuit during the existence of the inter-fen ence.

Various means have been proposed for neutralizing the effects of these disturbances. One is shown in the patent to A. B. Clark, 1,126,956, dated February 2, 1915, in which the current, set up in a pilot wire exposed to the same interference as the sig naling circuits, is used to control a generator in the ground lead of the signaling circuits whereby a neutralizing potential will be set up in the said signaling circuits whenever foreign interference-sets up a difference. of potential simultaneously in the signaling circuits and in the pilot wire. An improvement upon this method is shown in the copending application of Cory, Serial No. 512,379, filed March 9, 1922, in which an artificial network, and a control relay performs the function of the pilot wire in the Clark arrangement.

One of the objects of my invention is: to provide an arrangement for neutralizing the effects of foreign interference upon the grounded signaling circuits in which the current setup in apilot circuit by a source of interference .will be impressed upon an auxiliary winding connected with the receiving devices of the line circuit-s, the magnitude of the neutralizing current being controlled so that its effect upon the re ceiving devices will be equal and opposite to that caused by the said source of interference in the said. line circuits.

Serial No. 562,146.

Other objects of this invention will be apparent from the following description when read in connection with the attached drawing, of which Fig. 1 shows one form of embodiment of the invention; Fig. 1 shows a detail of the battery switching mechanism applicable for example to the embodiment shown in Fig. 1; and Fig. 2 shows another form of embodiment which differs from'Fig. 1 in the use of polar relays instead of artificial networks in the pilot circuit.

In Fig. 1, 1 and 2 represents the line wires of two grounded telegraph circuits extending from station A (shown in the figure), to a distant station (not shown), and terminating there in a circuit preferably substantially similar in form to that shown in Fig. 1. A pilot wire 3 extends parallel to the wires 1 and 2 from station A to the distant station so as to be exposed to the same source of interference, and is terminated there either in an apparatus similar to that shown in Fig. 1, or through a grounded impedance. The line 1 is con nected with one terminal of the main winding 4 of a differential duplex relay 8 located at station A. The midpoint of winding 4 is connected with the tongue 9 of the pole changer 10 by means of which signaling impulses of the proper polarity may be transmitted over the said line circuit. to the distant station. Connected with the pole changer 10 is a line battery 11. A phn rality of taps are taken out. at different points of the said battery, terminating in the contact points 12-, 12, etc, with which the contact arm 13 is adapted to cooperate, so as to cause current to flow through one half of each main winding of the line relays, for a purpose which will be made clear hereinafter. An artificial line let is connected between the contact arm 13 andt-hc said terminals of the winding 4 in order to balance the real lines.

The line 2 is similarly connected with the winding 5 of the differential relay 15, the midpoint of which is connected with the tongue 16 of the pole changer 17 connected with the grounded battery 11. The line relays 8 and 15 have connected therewith auxiliary windings 18 and 19 respectively which are connected in series with a grounded battery 20 and a current limiting resistance 21,

a relay 22 and the plate 23 of a thermionic vacuum tube The filament 25 of thcsuid vacuum tube is grounded so that when the filament is heated current will flow from the grounded battery through the windings l8 and 19 of the relays 8 and 15 respectively,

through the winding of the relay 22, and

across the gap between the plate 23 andthe filament 25. The magnitude of this current may be controlled either by the resistance 21 or by the temperature of the filament which can be regulated by thebattery 26. The pilot wire 8 is connected with the impedances 6 and 7, which are intended to resemble electrically the impedance of the ter minal equipment connected with the real line circuits 1 and 2.

Since there is considerable coupling between the various circuits it is desirable that the terminating impedance be the same for all of the circuits, A variation in the terminal impedance of any circuit will afiiect the impedance of all circuits coupled with it. The magnitude of impedances 6 and 7 '3 connected with the pilot wire 3 may be determined in the following manner: Let it be 'assumed that the terminal apparatus connected with any line circuit, such as 1, coin sists of a differential relay, a transmitter branch and a balancing network, connected in the usual manner. If a composite set is connected with the line circuit 1, in order to render this circuit available also as part of a telephone circuit, the set should be considered as part of the line and not as part of the terminal apparatus, for the purpose of estimating the magnitudeof the impedances 6 and 7. Since the space current which flows through the auxiliary windings 18 and 19 of relays Sand 15 respectively, is normally of such magnitude as to neutralize the current from the line, there is no net magnetizing action of the cores of the relays 8 and Consequently, the relay impedances may be assumed to-be pure resistance, and the current in such circuit is proportional to the voltage. Now, it we were to use a relay in the pilot circuit 3, as is used in lines 1 and'2, we must have a coinpensat ing winding on that relay also. The same purpose may be accomplished, however, by removing the pilot wire relay and substituting resistances in its place. A practical requirement arises, however, from the fact that it is desirable to have the filament grounded;

he impedance 7 is connected to the battery 28 having its positive pole grounded so that its negative pole will be connected with the grid 27 of the vacuum tube. I

To determine pro )er values of inrped-ances to be used for networlrs (3 and .7, I proceed as follows: 7

The impedance of the network 6 may be denoted by the symbol Z, and the impedance oil the network 7 may lac-denoted by the symbol The first requirement is that the total impedance of these two netwonks shall be equal to the terminal impedance of the telegraph circuits in the ollice. It is well known in the art that the terminal impedance of a degree of The second condition is that the volt-age drop across shall equal the corresponding drop over the wholeor the dillerential relay, assuming that the windings are non-inductive. This gives as the second condition for determining the values of Z and a:

ZE L 2R 2L T Z +2 Solving these equations gives and - vT R Z (L+R+T R+L In practice it will be found necessary to brmg about only an approximate fulfillment of these relations.

Since current flows continuously from the positive battery 20 through the windings l8 and 19 of the relays 8 and 15 respectively. it is necessary to provide some means rm? neutralizing the eli'ect oi. this continuous current upon the differential relays so that the said relays will not bebiased thereby. This may be done in many different ways, of which one is shownin the drawing. in this arrangement, the main line battery 11 effects the neutralization of the spacecurrent effect and thereby renders the relays unaffected by this continuous and uninterrupted flow of current. It will be seen that the artificial lines let and 29 are connected between the main line batteries 11 and onehalf of the main windings l and 5 of the relays 8 and'15 so that current will flow through the said halves 01 the windings in such direction and will be of such magnitude as to counteract the eiiect of the current that flows normally through the auxiliary windings which are connected with the vacuum tube device 24:. y

Having in n'rind the foregoing description of the parts of the circuit shown in Fig. 1, this invention will be clearly understood from the following description of the mode of operation of the circuit.

Let it be assumed that a difference of potential exists between the ground points at opposite terminals of each of the line circuits 1 and 2 of the pilot circuit 3, so as to cause a flow of current from thedistant station to the station A over the said circuits. This interfering current will flow through the main windings 1 and 5 of the relays 8 and .15 respectively and will tend to move the tongues of the receiving relays, thereby interfering with the transmission of signals over the line circuits. Furthermore, let it be assumed that the vacuum tube2d had been adjusted so that current of a certain strength flows through the circuit containing the windings 18 and 19. Since the pilot circuit 3 is exposed to the same difference of interfering potential as the lines 1 and 2, current will flow over the circuit 3 in the same direction and of the same magnitude as the interfering current in the lines 1 and 2. This current will cause a variation of potential of the grid 27 which will vary the flow of current in the windings 18 and 19 by virtue of the variation of the electron flow betweenthe plate 23 and the filament 25 of the vacuum tube 2 1. The magnetomotive force'set up by this flow of current through the auxiliary windings 18 and 19 will neutralize the magnetomotive force set up in the windings .4 and 5 by current from the same interfering potential that caused the current flow over the pilot wire 3. When the disturbance diminishes in intensity the space current in the vacuum tube 24 will become less, and consequently the magnetomotive force of the windings 18 and 19 will diminish. 7 By proper adjustment of the normal potential of the grid 27 by means of the negative battery 28 the effects of interti'cring potentials may be neutralized in the receiving relays 8 and 15 regardless of the direction of the flow of the interfering cur rent in the said lines and regardless of its magnitude.

It may be desirable to neutralize only relatively small interference effects by the space current'of the tube itself and to allow the greater effects to be taken care of by means of'current from another source which will be controlled by the said space current. This may be done by means of the polar relay 22 in series with the output circuit of the vacuum tube. Such a relayis adapted to control the contact arm 13 arranged to move over the contact points 12, 12, etc., of the grounded battery 11. 'A relay adapted to perform such function is shown in Fig. 1. The normal space current from the vacuum tube 24 will be sufficient when flowing through thewinding of the relay 22 to hold its armature in a position midway between the contacts 51 and 52. Connected with the armature 50 is one terminal of the battery 53, the other terminal of which .is connected with one end of the windings 5i and 56 of the relays 5.) and 57, respectively. The other ends of the said windings are connected with the contacts 51 and 52 re spectively. The armatures 69 and 70 of the relays are joined by means of the V-shaped structure 58, the upper end of which, 59, is pivoted to the arm 60, which rests upon a frictionless support 61. lVhen the relays are not energized, the device 58 is moved up and down by the continuously rotating device 64, which is connected with the other end of the arm 60 at the point 62 by means of a connecting link 63. The lower ends of the sides of the V of the device 58 which are hookshaped, as indicated at 65 and 66, are adapted to cooperate with the projecting points 68 of the rotatable member 67. Attached to the said member 67 are two arms 13 and 30 which are insulated from each other by the insulating segments 70. The arm 13 is adapted to cooperate with the contact points 12, 12, 12, etc., which are connected with the main line battery 11, as shown in Fig. 1, and the arm 30, is adapted to cooperate with the contact points 69, 69, etc., which are connected with the auxiliary battery 28, as shown in Fig. 1.

The mode of operation of this device is as follows: When the space current between the filament 25 and plate 23 of the vacuum tube 24, as shown in Fig. 1, reaches a predetermined value, the relay 22 will be operated, which will cause its armature 50 to touch either of its contacts 51 or 52, depending upon the direction of flow of current in the winding of the relay 22. If, for example, the armature 50 touches the contact 51, current will flow throughthe winding 5% of the relay 55, thereby attracting the armature 69, which results in moving the hooked end 66 under the pins 68, which would tend to move the rotatable member 67 in a counter-clockwise direction. The effect of this is to move the arms 13 and 30 in a similar direction, thereby increasing the potential applied by the arm 13 through the artificial lines and one-half of each of the main windings of the polar relays, thereby counteracting the effect of the increased space current that flows through the auxiliary windings of the said relays. Simultaneous with the movement of the arm 13 the arm 30 is also moved across its contact points 69, thereby increasing the negative charge upon the grid 27, which tends to cut down the space current. It will be seen that by means of an arrangement as shown in Fig. 17" or an equivalent structure, excessive interference currents set up in the lines 1, 2, etc, may be controlled mainly n at by means of the line battery 11, leaving the vacuum tube 2 1 to care for only the slight variations in Voltage set up in the said lines. \Vhen the line voltage drops below acertain predetermined value, the armature 50 of the relay 22 will move into contact with its contact point 52, thereby energizing the relay 57, which attracts its armature 70. This results in a movement of the arms 13 and 30 in the opposite direction, thereby diminishing the current from the main battery 11 through the main windings of the polar relays and diminishing the negative char e upon the grid of the vacuum tube 24:, which increases the space current through the circuit connected therewith.

The arrangement shown in Fig. 2, in which the same reference numerals have been used torepresent parts which are the same as in Fig. 1, differs mainly in the method and means for controlling the .grid voltage of the vacuum tube. The pilotwire 3 is connected with one terminal of the winding 31 of a differential relay, to the other terminal of which is connected an artificial line Connected with the midpoint of the winding is an impedance 83, which simulates the transmitter branch impedance. This impedance is connected with the main battery 11 and the same voltage is applied thereto as is applied to the artificial line 32-. Associated with the main winding 31 is an auxiliary winding 35, which is bridged across an impedance 36 of the cir-' cuitthrough which the space current flows.

The magnitude of this impedance is so fixed that the same current flows through the winding 35 as flows through the windings 18, 19, etc, of the relays 8 and 15 respectively. From the foregoing description it will be seen that the terminal equipment of the pilot wire 3 simulates the equipment connected with the signaling circuits 1,2,

7 etc.

The mode of operation of the foregoing hen no interfering circuit is as follows: currents are present in the signaling circuits 1, 2, etc, or in the pilot wire 3, a space current of a predetermined value will fiow from the plate 28 through the winding of the relay 22, the impedance 36, the windings. ll, 19 and 18 of the relays 15, 15 and 8 respectively, and back to the tilunent 25:,

this current resulting from the s-pacebat-' tery 20. This current would tend to bias the relays 8, 15, 15, etc, were it not for current flowing from the battery 11 througli the artificial lines 14;, 29, etc., and. thence over one-half of the main windings 10, 5, etc, of the relays 45, 15, etc. These currents tend to o-tl'set each other in their eil ects upon the armature of the relays and therefore prevent any biasing that might tend to arise- When an interfering current is set up in the signaling circuits 1, 2, etc, by

virtue of some foreign interference, a similar "current will be set up in the pilot wire 3 and the direction of this current will con trol the polarity of the grid 27. The interfering currents in the signaling. circuits 1, 2, etc., will tend to flow through the wind lugs 1, 5, etc., of their relays and through the artificial line to ground through the battery 11. The effect of this current upon the receii' 'ing relays will be neutralized by means 01 current variations set up in the circuitcontaining the auxiliary windings 18, 19, etc, by virtue of the control of the space current between the plate23 and the filament 25 by means of the grid 27, whose charge has been varied by the same interfering current upon the pilot wire 3.

The arrznigement shown in Fig. 1 is adapted to be used also in connection with the circuit arrangement shown in Fig.2, and operate in substantially the same manner. Since the aifiangement functions when used in connection with Fig. in substantiallv the same manner in which it operates in colinection with Fig. 1, it is not believed that further description necessary.

. The principal difference between the at rangen'ients shown in Figs. 1 and 2 is in the manner of deriving the control voltage for the grid. In Fig. 1, the drop of potential over a network has been utilized for this purpose. In F 2, the terminating equip ment of the pilot line is made similar to the corresponding eqi-iipinent for the regular telegraph lines, and the (lGIlVGCl'CMltlOl1 0:- age is equal to the voltage to be neutralized. lVith this arrangement non-grounded batteries should be used.

t will be seen that by means of my invention the effects of foreign potentials upon grounded signaling ciifcui'ts may be substantially neliitralized and the circuits rendered tree from interference.

Although the inventio'i'i has been disclosed as embodied in groundial telegraph circuits hating polar relays connected therewith, the invention is not liin'itcdto this [uriticula r form of circuit nor to the particulz-ir form of ceiving relay connected therewith, the said circuit being connected with one of the windings, a pilot circuit substantially coextensive with said signaling circuit, hotlr oil? 1 said circuits being subjected to substantially the same different-es ot earth potential, a vacuum tube having its grid connected with the pilot circuit and having its plate circuit comiccted with another of the said windings llu of the receiving relay and having a source of direct current connected therewith, the method of substantially neutralizing differences of ground potential in the signaling circuit which consists in impressing upon the grid of the vacuum tube the earth potential set up in the pilot circuit and in opposing in the receiving relay the variations of the plate current against the variations set up in the signaling circuit by the same difference of earth potential.

2. In a system comprising a grounded signaling circuit having a muitiwinding receiving relay connected therewith, thesaid circuit being connected with one of the windings, a pilot circuit substantially coextensive with said signaling circuit, both of said circuits being subjected to substantially the same differences of earth potential, a

vacuum tube having its grid connected with ences of ground potential in the signaling circuit which consists in allowing the said earth potentials to be set up in the signaling and the pilot circuit simultaneously, 11npressing the potentials in the pilot circuit upon the grid of a. vacuum tube and 1mpressing the resultant space current var ations due to variations of grid potential upon one of the windings of the receivmg relays so as to neutralize the effect of the earth currents through the other winding of the said relay.

3. In a system for neutralizing foreign potentials in signaling circuits, the combination with a signaling circuit having a relay associated therewith, of a pilot circuit, and a vacuum tube controlled by the said pilotcircuit and adapted to neutralize currents resulting from foreign potentials impressed upon the relay by the said signaling circuit.

4:. In a system for neutralizing foreign potentials in signaling circuits, the combination with a signaling circuit having a relay with mainand auxiliary windings associated therewith, of a pilot circuit and a vacuum tube controlled by the said pilot circuit and. adapted to impress current upon said auxiliary winding of such .magnitude and in such direction as to neutralize the- .intcrfering ctu'rent set up in the main winding by the said signaling circuit.

5. In a system for neutralizing foreign potentials in a signaling system, the combination with a signaling circuit of a relay having main and auxiliary windings, a pilot circuit, a vacuum tube controlled by the said pilot circuit and adapted to cause its normal space current to flow through said auxiliary winding, and another source of current connected with the said main winding to neutralize the effect of the said normal space current, thereby eliminating biasing of the said relay.

6. In a system for neutralizing foreign potentials in a signaling system. the combination with a relay having main and auX- iliary windings, of a real line circuit and an artificial line, both connected with said main winding, a pilot circuit subiected to the same electrical exposure as said real line, a vacuum tube-connected with the said pilot circuit and said auxiliary winding, whereby the elfcct of interfering currents transmitted through said main windings may be neutralized.

7. In a system for neutralizing foreign potentials in a signaling system, the combination with a relay having a plurality of windings, of a line circuit and an artificial line connected with opposite terminals of one of the said windings, a pilot circuit adapted to have set up therein the same interfering potentials as the said line circuit, and a vacuum tube having its grid connected with said pilot circuit and its plate connected with another winding of said relay, whereby interference effects therein may be neutralized.

.8. In a system for neutralizing foreign potentials in a signaling system, the combination with a line circuit having a terminal circuit connected therewith comprising a. relay having main and auxiliary windings, an artificial line, a transmitter branch having a source of potential associated therewith, of a pilot circuit exposed to the same interference as said line circuit and having a plurality of resistance networks associated therewith, simulating the said terminal circuit, and a vacuum tube connected with said auxiliary windings and with said networks so that the space current will be controlled by interfering potentials in the said line circuit.

9. In a system for neutralizing foreign potentials in a signaling system, the combination with a relay having main and auX- iliary windings, of a line circuit, a pilot circuit having a network associated therewith, a vacuum tube controlled by the said pilot circuit and adapted to apply space current to the said auxiliary winding, and switching inc-ans controlled. by the said spacc'current to supply part of the neutralizing current when the space current exceeds predetermined limits.

10. In a system for neutralizing foreign potentials in signaling circuits, the combination with a signaling circuit having a polar relay associated therewith, of a pilot circuit substantially coextensive with the said signaling circuit, and a vacuum tube controlled by the said pilot circuit, and adapted to neutralize currents resulting from foreign potentials impressed upon the said polar relay bythesaid signaling circuit.

11. In a system for neutralizing foreign potentials in signaling circuits, the combination with a signaling circuit having a receiving device associated therewith, of a pilot circuit, substantially coextensive with the said signaling circuit, and a vacuum tube controlled by the said pilot circuit and adapted to neutralize currents resulting: from foreign potentialsimpressed upon the said receiving device by the said signaling circuit.

12. The method of neutralizing foreign interfering potentials in grounded signaling circuits, which consists in allowing the said potentials to be set up in the saidsignal ing circuits and in a pilot Wire simultaneously, impressing the potentials set up inv the pilot wire upon the grid of a vacuum tube, impressing the resultant space current variations upon the receiving device connected With the said signaling circuit in such Way as to neutralize the currents also set up in the said receiving device by interference in the said signaling circuits.

In testimony whereof, I have signed my name to this specification this 17th day of- May, 19:22.

HARRY N YQUIST. 

